I have a 1998 Ford F250 pickup with 4.6L V8, stick shift and 112,000 miles. It knocks on 87 octane and the knocking is getting worse. Of course I can reduce it greatly with 93 octane, which is must when I pull my camper. The owner’s manual says to ignore “light knock”, but there’s no way to identify what that means. I was wondering if this could be controlled with a colder plug, assuming that one is available. Any suggestions?
Over time, carbon build up increases the compression of the engine, and this increases the likely hood of knock on low octane gas. All three of the 4.6L cars that I had required 89 octane or higher to keep them from knocking (pinging really).
You could try some Seafoam to see if it might clean out some of the carbon. Also, check the EGR passages and valve. If the EGR is stopping up, it can cause the knocking too.
Most of the time this problem is EGR related. EGR electronics, faulty EGR valve, clogged EGR passages, etc.
I’m not a fan at all of those manual recommendations about ignoring light knocking as someone’s interpretation of what constitutes light can vary a lot.
Some chronic, long term light knocking and next thing you know pistons may start disentegrating.